Support ADT types in type info reflection

[SpriteOvO]

Tracking issue: #146922 #![feature(type_info)]

This PR supports ADT types for feature type_info reflection.
(It's still a draft PR, with implementation in progress)

Note that this PR does not take SemVer into consideration (I left a FIXME comment). As discussed earlier (comment), this requires further discussion. However, I hope we could get an initial implementation to land first, so we can start playing with it.

Progress / Checklist

• Struct support.
• More info for Struct.
• Enum
• Union
• Rebasing PR to main branch
  (It's currently based on PR Support primitives in type info reflection #151123, so here's an extra commit)

r? @oli-obk

[rustbot]

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[SpriteOvO]

I feel like I should write sym::Some discriminant for name? 🤔 Writing ptr directly seems to work, but this relies on how Option<&'static str> is underlyingly represented IIUC.

But const eval interpreter doesn't complain about this -- perhaps it should?

[rust-log-analyzer]

The job aarch64-gnu-llvm-20-2 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

fmt: checked 6650 files
tidy check
tidy [rustdoc_json (src)]: `rustdoc-json-types` modified, checking format version
tidy: Skipping binary file check, read-only filesystem
tidy [style (compiler)]: /checkout/compiler/rustc_const_eval/src/const_eval/type_info.rs:77: TODO is used for tasks that should be done before merging a PR; If you want to leave a message in the codebase use FIXME
tidy [style (compiler)]: /checkout/compiler/rustc_const_eval/src/const_eval/type_info.rs:354: TODO is used for tasks that should be done before merging a PR; If you want to leave a message in the codebase use FIXME
tidy [style (compiler)]: FAIL
tidy [alphabetical (compiler)]: /checkout/compiler/rustc_span/src/symbol.rs:1081: line not in alphabetical order (tip: use --bless to sort this list)
tidy [alphabetical (compiler)]: FAIL
tidy: The following checks failed: alphabetical (compiler), style (compiler)
Bootstrap failed while executing `--stage 2 test --skip tests --skip coverage-map --skip coverage-run --skip library --skip tidyselftest`
Command `/checkout/obj/build/aarch64-unknown-linux-gnu/stage1-tools-bin/rust-tidy /checkout /checkout/obj/build/aarch64-unknown-linux-gnu/stage0/bin/cargo /checkout/obj/build 4 yarn` failed with exit code 1
Created at: src/bootstrap/src/core/build_steps/tool.rs:1612:23
Executed at: src/bootstrap/src/core/build_steps/test.rs:1357:29

Command has failed. Rerun with -v to see more details.
Build completed unsuccessfully in 0:00:52
  local time: Wed Jan 14 21:40:41 UTC 2026
  network time: Wed, 14 Jan 2026 21:40:42 GMT
##[error]Process completed with exit code 1.
##[group]Run echo "disk usage:"